DC-DC Converter

The power losses in a power electronic DC-DC converter can be divided into conduction and switching losses, where conduction losses consist of inductor conduction losses and MOSFET conduction losses [28] (Fig.14.7).

• Inductor Conduction Losses Inductor conduction losses is as follows

Pl = I2L x Rl {14.17)

where Rl is the DC-Resistance of the inductor,

The inductor rms current (IL):

D/2

11 = /2 + (14.18)

where /o the output current and D/ the ripple current.

Typically, D/ is about 30 % of the output current. Therefore, the inductor current can be calculated as:

/l = /o x 1.00375 (14.19)

Because the ripple current contributes only 0.375 % of IL, it can be neglected. The power dissipated in the inductor now can be calculated as:

Подпись: (14.20)Pl = /o2 x Rl

• Power Dissipated in the MOSFETs

The power dissipated in the high-side MOSFET is given by:

PQ1 = /2nnS_Q1 x RDSON1 (14-2ї)

DC-DC Converter DC-DC Converter

where Rdson1 is the on-time drain-to-source resistance of the high-side MOSFET.

DC-DC Converter Подпись: (14.24) (14.25) (14.26) (14.27)

where Rdson2 is the on-time drain-to-source resistance of the low-side MOSFET.

and:

L = Inductance (H) f = Frequency (Hz)

Table 14.5 Investigated appliances, appliance ratings and estimated on time per day

Product name

Quantity

Ratings

Power rating (W)

Current rating (A)

Voltage Rating (V)

Appliance on time in a day

Light bulb LED

4

7

0.60

12 DC

10

Light bulb CFL

2

12

1.00

12 DC

10

Microwave oven

1

235

10.00

24 DC

1

Induction stove

1

2000

10.00

230 AC

2

Electric geyser

1

1500

8.00

230 AC

1

Sandwich maker

1

550

23.00

24 DC

0.5

Coffee maker

1

135

11.00

12 DC

0.5

Refrigerator

1

72

3.00

24 DC

12

(DC)

Water purifier

1

11

0.50

24 DC

1

Ventilation fan

4

20

0.90

24 DC

5

Submersible

1

240

10.00

24 DC

0.5

pump

Washing

1

70

3.00

24 DC

0.5

machine

Vacuum cleaner

1

95

8.00

12 DC

0.25

Window unit AC

2

800

33.30

24 DC

12

Laptop

1

65

3.34

19.5 DC

7

Perdonal

1

170

14.00

12 DC

5

computer

External modem

1

5

0.43

12 DC

24

15.6’’LCD

1

30

2.50

12 DC

5

television

Ceiling fan

4

20

1.70

12 DC

4

Hair dryer

1

425

15.00

24 DC

0.5

Cell phone

4

4

0.30

12 DC

5

Hybrid car

1

3000

12.50

240 DC

10

Подпись: Fig. 14.8 Cable size versus prices in Indian scenario
image232

VIN = Input voltage (V) Vo = Output voltage (V)

• MOSFET Conduction Losses

Product Name

Cable Size (mm2)

Cable length (meter)

Energy Loss in feeder (kWh/yr)

Total Energy Consumption (kWh/yr)

Light Bulb LED

4

40

0.23

102.43

Light Bulb CFL

4

30

0.47

88.07

Microwave oven

6

10

1.05

86.82

Induction Stove

1.5

20

16.74

1476.74

Electric Geyser

1.5

30

8.04

555.54

Sandwich Maker

35

20

0.95

101.32

Coffee Maker

25

20

0.30

24.94

Refrigerator DC

4

20

3.39

318.75

Water Purifier

1.5

20

0.02

4.04

Ventilation fan

1.5

30

0.51

146.51

Submersible Pump

6

10

0.52

44.32

Washing Machine

6

25

0.12

12.89

Vacuum Cleaner

16

15

0.09

8.76

Window Unit AC

25

10

33.42

7041.42

Laptop

10

40

1.96

168.04

Personal Computer

25

15

3.69

313.94

External Modem

1.5

30

0.56

44.36

15.6’’ LCD Television

6

20

0.65

55.40

Ceiling Fan

4

20

0.36

117.16

Hair Dryan

16

15

0.66

78.22

Cell Phone

1.5

20

0.04

29.24

Hybrid Car

1.5

10

65.40

11015.40

Total Energy in kWh/year

139.17

21834.31

Table 14.6 Cable size, power loss and energy consumption for DC system

Подпись: PFET DC-DC Converter DC-DC Converter Подпись: (14.28)

For typical buck power supply designs, the inductor’s ripple current, DI, is less than 30 % of the total output current, so the contribution of DI2/12 to the is negligible and can be dropped to get:

Note that when RsDON1 = RsDON2, then:

PFET = iO x rsdon2 (14.29)

The power dissipated in the MOSFET is independent of the output voltage. By using Eq. (14.29) the conduction losses of MOSFET can be calculated at any output voltage. On the other side, inductor conduction losses and switching losses etc. are independent of output voltage and remains constant with change in output voltage [22].

DC-DC Converter

Hence, PD now can be computed as:

PD = PL + Pfet + otherlosses (14.30)

Подпись: g DC-DC Converter Подпись: (14.31)

There are some other types of losses such as the MOSFET switching losses, quiescent current etc. At any output voltage, the overall efficiency can be calcu­lated by the known total power supply losses and power supply output power.

Updated: October 23, 2015 — 12:41 pm